The generator stator core is the largest monobloc component in a turbine-generator set. The stator core comprises thousands of thin steel laminations that are stacked and clamped together to form a cylindrical stator core. Each lamination defines a central opening and thus when stacked together the opening extends the axial length of the core. A rotating rotor within the opening generates electric current in stator windings that are wound into the core.
Steady-state and transient forces generated during normal operation and transient conditions distort the core geometric shape. Improperly attaching the core to the frame can cause lamination vibrations due to magnetic impulses and core elliptical dilation (i.e., distorting the core from a circle to an ellipse). The core dilation effect is more prevalent in two pole generators (inducing a two lobe core distortion) than in four pole generators (inducing a four lobe core distortion). Also, mechanical fatigue effects caused by the vibrations can lead to premature failure of the generator.
It is known, for example see commonly-owned U.S. Pat. No. 5,875,540 incorporated herein by reference, to overcome some of the problems with prior art assembly techniques by first assembling then joining a number of laminations, collectively referred to as a donut. A plurality of these donuts are then stacked (vertically or horizontally) to form the stator core. This process saves substantial time when compared with individually assembling the laminations and also produces fewer core flaws.
When individual laminations or a plurality of laminations in the form of a donut are formed into a core, they engage axially-extending keybars disposed on an inside surface of the generator frame. The keybars are rod-like or bar-like members that extend a length of the frame and attach to internal frame structures (e.g., frame rings). An inwardly-facing surface of the keybar comprises a projection that engages axial grooves in the outer circumference of the laminations (donuts).
FIG. 1 is a cutaway view of a generator frame 2 prior to insertion of the laminations or donuts. Keybars 6 run an internal axial length of the frame 2 and are generally attached to the support rings 4 via a transition adapter plate 5 (see FIG. 2). The support rings 4 are attached to the generator frame 2 as illustrated in FIG. 1.
The laminations and keybars are engaged with complementary grooves as shown in FIG. 2, illustrating a dovetail keybar profile. Each lamination 10 defines a plurality of notches 12 about a circumference of the lamination. The notches 12 match a complementary profile of the keybar 6. When a plurality of laminations is attached together, the aligned notches form an axial groove. Thus several axial grooves are disposed about a circumference of the core. By sliding the laminations 10 onto the keybars 6, the laminations 10 are secured to the generator frame 2. Since the stator core vibrates during operation, it is critical for the keybars and any keybar attachments to be rigidly attached to the core and to the generator frame.
Since the laminations may be mounted individually or as donuts, if the fit between the lamination grooves 12 and the keybars 6 is too tight, field installation can be very difficult or, in the extreme, impossible. Thus there is a need for structural elements and processes that permit the laminations or donuts to be easily placed onto keybars then secured to the generator frame.
Those skilled in the art recognize that given the wide variety of available generator styles and ratings, there exists a wide variety of generator frame constructions, stator constructions and core attachment elements. It is desired to provide technically sound (i.e., providing the required structural rigidity while also limiting frame vibrations) and expedient techniques and structural members for attaching the core to the frame.